The shape of a tubular or closed loop workpiece makes operator handling difficult and cumbersome. Often, such workpieces must be sewn by hand or are manually guided to the stitch forming means of the sewing machine to assure proper workpiece fabrication. Even though guides may be used in some applications, such manually manipulation is timely and expensive.
On those devices where the workpiece edge is automatically sewn, workpiece edge alignment is achieved only within a predetermined range. Because the workpiece advancement is often halted in such automatic operations, the sewing unit has a relatively long cycle time. Also, with such devices, manual skill remains necessary in order to insert the workpiece and to position it correctly. Tubular workpieces having a wavy or ragged edge cannot be satisfactory processed on such known sewing units.